Si Ohmic Contacts Research Articles

Role of ultra-thin tungsten interlayer in blocking nitrogen diffusion and reducing specific contact resistivity in titanium/n+-Si ohmic contacts

Role of ultra-thin tungsten interlayer in blocking nitrogen diffusion and reducing specific contact resistivity in titanium/n+-Si ohmic contacts

Insertion of Hafnium Interlayer to Improve the Thermal Stability of Ultrathin TiSi x in TiSi x /n+-Si Ohmic Contacts

Insertion of Hafnium Interlayer to Improve the Thermal Stability of Ultrathin TiSi_<i>x</i> in TiSi_<i>x</i>/n⁺-Si Ohmic Contacts

Exploration of the impact of interface states density on the specific contact resistivity in TiSix/n+-Si Ohmic contacts through high-low frequency method

In our previous work, a reduction of specific contact resistivity (ρc) in TiSix/n+-Si Ohmic contacts by ∼21% has been achieved with proper Ge Pre-amorphization Implantation (PAI). In this work, the mechanism behind such an improvement using Ge PAI is explored experimentally. Versatile characterizations including current–voltage (I–V), capacitance–voltage (C–V) measurements and cross-sectional transmission electron microscopy (XTEM) are performed and analyzed. High-low frequency method is used to extract the responsive interface states density (Dit) of TiSix/n-Si Schottky diodes with and without Ge PAI. It is demonstrated that in TiSix/n+-Si Ohmic contacts, the ρc reduction by ∼21% with Ge PAI should be ascribed to the reduction of Dit at TiSix/n-Si interface. From the distribution of Dit, it can be inferred that a part of shallow level defects can be annihilated after annealing for TiSix/n-Si with Ge PAI, but deep level traps still exist. A further discussion about the relationship between Dit and ρc is tentatively provided.

Boron Implanted Junction with In Situ Oxide Passivation and Application to p‐PERT Bifacial Silicon Solar Cell

Boron junction and its passivation is an active topic in photovoltaic research due to its importance to passivated emitter and rear totally‐diffused (PERT) bifacial Si solar cell. In this paper, a systematic study on boron‐implanted junction, its passivation and ohmic contact formation, as well as application to p‐PERT bifacial cells has been presented. More specifically, the impact of junction profile and surface passivation on boron junction quality, which can be influenced by implantation and in situ oxidation anneal parameters is studied. Good‐quality boron emitter and metal/p+‐Si ohmic contact are achieved, as demonstrated by emitter saturation current of 5–30 fA cm−2 and specific contact resistance of 3–6 mΩ cm−1. A roadmap for a p‐PERT bifacial cell using fully ion implanted (boron and phosphorus) technology, based on which p‐PERT bifacial cells demonstrats front side efficiency of 20.6% (open circuit voltage of 658 mV), rear side efficiency of ≈17% and bifaciality factor of 0.82–0.87 is also presented. Effective cell efficiency of ≈22% is achieved with a Halm IV‐tester with white transporting belts that enhance reflection about 10% from the cell rear.

3D wafer level packaging technology based on the co-planar Au–Si bonding structure

Driven by ever-growing demands on 3D integration, various state-of-the-art electronics packaging techniques have been developed. This study presents a novel and cost-efficient 3D wafer level packaging technology based on co-planar Au–Si bonding structures, whose two remarkable features are (1) eliminating the height difference derived from multi-layer metal interconnection lines crossing bonding rings by building co-planar bonding structures and (2) accomplishing vertical interconnections of low-resistivity Si column structures by forming Au–Si bonding ohmic contacts. In this paper, the packaging structure is interpreted by designs, fabrications and tests, in which the efficiency verification on co-planar bonding structures and vertical interconnections is concretely addressed. The performances on co-planar bonding structures have been revealed by 3D profiles of bonding surfaces, cross-sectional SEM images (the gap-free bonding layer) and tensile tests for Au–Si bonding strength. Besides, tests on leak rates of packaged chips indicate good packaging hermeticity. In terms of vertical interconnection properties, an in situ extracting method on the specific contact resistance (ρc) is also introduced to quantitatively appraise the quality of Au–Si ohmic contacts. Therefrom, the measured resistance of a vertical interconnection (~1 Ω) could be qualified for most devices’ interconnection requirements. And further, the extracted ρc values of 1.83–3.48 × 10−8 Ω · m2 also imply forming of good ohmic contacts in Au–Si bonding. More importantly, being analogously conducted by any available eutectic bonding techniques, this 3D packaging method has inherently extensive application prospects.

Comparative Study of the Current Transport Mechanisms in Ni&lt;sub&gt;2&lt;/sub&gt;Si Ohmic Contacts on n- and p-Type Implanted 4H-SiC

The knowledge of the temperature behavior of Ohmic contacts is an important issue to understand the device operation. This work reports an electrical characterization as a function of the temperature carried out on nickel silicide (Ni2Si) Ohmic contacts, used both for n-type and p-type implanted 4H-SiC layers. The temperature dependence of the specific contact resistance suggested that a thermionic field emission mechanism dominates the current transport for contacts on p-type material, whereas a current transport by tunneling is likely occurring in the contacts on n-type implanted SiC. Furthermore, from the temperature dependence of the electrical characteristics, the activation energies for Al and P dopants were determined, resulting of 145 meV and 35 meV, respectively. The thermal stability of the electrical parameters has been demonstrated upon a long-term (up to ~100 hours) cycling in the temperature range 200-400°C.

Ni, NiSi&lt;sub&gt;2&lt;/sub&gt; and Si Secondary Ohmic Contacts on SiC with High Thermal Stability

A method for formation of enhanced ohmic contacts on SiC for operation under adverse conditions has been studied. Ni, NiSi2 and Si ohmic contacts were prepared and tested at 300°C on air for hundreds of hours. NiSi2 and Si showed high thermal stability. Moreover, also the so called secondary contacts showed preserved good electrical and structural properties in the thermal test. The secondary ohmic contacts are formed from original ohmic contacts after they are etched off and replaced with new ones. Secondary ohmic contacts originate in a certain surface modification of the SiC substrate created during high temperature annealing of the original contact. All applied contact materials enable formation of quality secondary contacts which is especially noteworthy at NiSi2 and Si. The results bring new SiC device design perspectives with the application of secondary ohmic contacts. For example, the contact is designed so that the primary contact makes as good ohmic behavior as possible with the secondary contact providing further important contact properties as high corrosion resistance, wire-bonding simplicity etc.

Si ohmic contacts on N-type SiC studied by XPS

Si ohmic contacts on N-type 4H- and 6H-SiC with contact resistivity comparable with Ni metallizations were prepared. After etching-off of the Si contacts and deposition of new, unannealed ones, good electrical parameters of the original contacts remain preserved. Such unannealed secondary contacts were already successfully created with original Ni or Ni silicide metallizations. An advantage offered by the secondary contacts prepared after the original Si contacts is that they are prepared on a high-quality SiC surface as the original Si does not react with SiC. XPS and AFM analyses were carried out. Under the original Si contacts when they are etched-off there is observed a shift of Si and C peaks to higher binding energies in comparison with a clean, bare SiC surface. After less than 2nm of the surface layer is sputtered-off the shift disappears. We suggest that preserved electrical parameters after the etching-off of the Si contacts stem from a SiC surface modification.

Temperature dependence of contact resistance for Au-Ti-Pd2Si-n +-Si ohmic contacts subjected to microwave irradiation

Based on a theoretical analysis of the temperature dependence of the contact resistance Rc for an Au-Ti-Pd2Si-n+-Si ohmic contact, a current-transfer mechanism explaining the experimentally observed increase in Rc in the temperature range 100–380 K is proposed. It is shown that microwave treatment of such contacts results in a decrease in the spread of Rc over the wafer and a decrease in the value of Rc whilst retaining an increase in Rc in the temperatures range 100–380 K.

The features of temperature dependence of contact resistivity of Au-Ti-Pd2Si-p+-Si ohmic contacts

We consider the features of formation of AuTiPd ohmic contacts to p + -Si. Metallization was made by vacuum thermal sputtering of Pd, Ti and Au films onto the Si substrate heated up to 330 С. It is shown that the contact resistivity increases with temperature; this is typical of metallic conductivity. We suggest that the ohmic contact is formed owing to appearance of shunts at Pd deposition on dislocations or other structural defects. The number of shunts per unit area is close to the measured density of structural defects at the metalSi interface. + -Si.

A silicon carbide thermistor

Abstract. We consider a silicon carbide thermistor with multilayer Au–TiB x –Ni 2 Si ohmic contacts intended for operation in the 77 to 450 K temperature range. Keywords: silicon carbide, thermistor, ohmic contact, buffer layer. Manuscript received 04.10.06; accepted for publication 23.10.06. 1. Introduction Silicon carbide (SiC) is a promising material for device applications (in particular, those involving arduous environmental conditions), and its thermal and radiation resistances are well documented. The SiC devices are usually used for extreme electronics when high temperatures and intense radiation are present. The main subject of this work was the implementation of SiC for development of a highly sensitive thermometer capable for use from liquid nitrogen temperatures up to 450 K and in the presence of ionizing radiation. It is well known that the radiation and thermal tolerances of semiconductor devices strongly depend on their design and the material properties, especially on the radiation and thermal resistances of the electrical contacts to the semiconductor elements. The preparation of reliable ohmic metal contacts to semiconductors operating at high temperatures or under radiation presents a difficult materials science problem. In the course of operation both under high radiation and in high temperature environment, the main mechanism of contact degradation is due to the mass transfer from the metal layer into the semiconductor element structure. The process of contact degradation may change the resistance and thermal sensitivity of sensors. Usually structure defects which are also produced by radiation in doped semiconductors have a small effect on the thermal sensor properties; they can strongly affect the sensor properties only after very high dose of irradiation. The ohmic contacts must therefore be chemically and physically compatible with the thermo-sensitive material over the operating temperature range and have similar resistance to the measurement environment of the thermometer. In the case of SiC thermometers, the formation of such contacts makes a considerable physico-technological problem since many of the metallic materials which are traditionally used as ohmic contacts form carbides and silicides when interacting with SiC, thus leading to nonuniform metal−SiC interfaces. As a result, the contacts are degrading in the course of operation at high temperatures. The degradation processes result in mass transfer of gold from the metallization layer into SiC through non-uniform metallic phase layers in the ohmic contact. Here we present our results on development of a SiC thermistor with multilayer Au–TiB

High voltage amorphous silicon TFT for use in large area applications

Previous work in high voltage amorphous silicon (a-Si) TFTs (HVTFTs) using an n+ μC–Si ohmic contact layer demonstrated that the soft contact TFT (SCTFT) design was a requirement for high voltage operation. In this research, conventional and high voltage TFT designs including the SCTFT are presented using an n+ a-Si contact layer. TFT ON-current measurements and series resistance extractions show that the conventional TFT performs equally well, if not better, at low and high voltages in comparison to all of the HVTFTs fabricated. The results indicate that the conventional space-efficient TFT design with an n+ a-Si contact layer is realizable for high fill-factor, high voltage applications such as direct detection, large area X-ray imaging. Also, the process reliability and performance for both conventional and HVTFT arrays can be improved for large area applications by the inclusion of an additional a-SiN layer.

Contact and via structures with copper interconnects fabricated using dual Damascene technology

A novel submicron process sequence was developed for the fabrication of CoSi/sub 2//n/sup +/-Si, CoSi/sub 2//p/sup +/-Si ohmic contacts and multilevel interconnects with copper as the interconnect/via metal and titanium as the diffusion barrier. SiO/sub 2/ deposited by plasma enhanced chemical vapor deposition (PECVD) using TEOS/O/sub 2/ was planarized by the novel technique of chemical-mechanical polishing (CMP) and served as the dielectric. The recessed copper interconnects in the oxide were formed by chemical-mechanical polishing. (dual Damascene process). Electrical characterization of the ohmic contacts yielded contact resistivity values of 10/sup -6//spl Omega/-cm/sup 2/ or less. A specific contact resistivity value of 1.5/spl times/10/sup -8//spl Omega/-cm/sup 2/ was measured for metal/metal contacts.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Very low resistivity Al [sbnd]Si ohmic contacts to boron-doped polycrystalline diamond films

The effects on the contact resistivity of annealing Al Si (99:1) contacts on diamond with different B concentrations have been investigated. The change of the current-voltage characteristic from rectifying to ohmic on lightly doped samples, and the drop of the contact resistivity by orders of magnitude for more heavily B-doped samples after annealing at 450 °C in N 2, are attributed to the formation of SiC at the metal-diamond interface. The existence of the SiC interface has been verified by X-ray-induced photoelectron spectroscopy. In addition, the contact resistivity is a very sensitive function of doping at high doping concentrations. Contact resistivities as low as about 10 −7 θ cm 2 have been achieved.

Structural and Electrical Effects on (A1-Si)/n+Si Ohmic Contact of in Situ Silicon Cleaning by Ar IONS Bombardment

ABSTRACTIn situ etching of native Si02 by Ar+ ion bombardment before metal sputter deposition can increase the contact resistance of the metal-semiconductor contact. This is commonly attributed to surface contamination produced by various mechanisms or to etch-induced surface damage. In this paper, in order to elucidate the cause of the increase of contact resistance, we have studied (Al-Si)/n+Si contacts prepared by various treatments of the Si surface. We attribute the higher postalloy contact resistance of the sputter etched contacts to the existence of an Al doped layer which formation was induced by the preexisting disordered layer created by the Ar+ ion bombardment.

Tungsten silicide barrier layers in aluminium ohmic contact systems

The barrier effect of sputtered tungsten silicide (WSi x ) layers for aluminium ohmic contact and interconnection systems is studied. The interfacial reaction of Al/WSi x /Si is measured using a 1.5 MeV He + Rutherford backscattering specrtometry technique after annealing at 450 and 500°C. Interfacial reaction does not occur. The leakage current of an n-p junction employing this ohmic contact is constant at 500°C and a stable interface can be achieved at 450 and 500°C. However, silicon precipitation takes place at the (Al-1%Si)-WSi x interface, but not when (Al-30ppmSi)-WSi x is used. This indicates that silicon precipitates arise from the Al-1%Si layer rather than from the WSi x barrier. Therefore a sufficient barrier effect, without silicon precipitation, can be achieved using Al-30ppmSi in place of Al-1%Si in Al/WSi x /Si ohmic contact systems.

A MODEL OF OHMIC CONTACT OF GaAs AND OTHER SEMICONDUCTOR

An inverse proportionality between the specific contact resistance ρc of n-type GaAs and its carrier concentration ND has been shown by a lot of experimental facts. In this paper, a comment is made on the various viewpoints about this phenomenon in the literatures and their shortages are pointed out as well. According to the band structure of ohmic contact, a new model, assuming that ρc consists of two parts (ρ(c1) and ρ(c2)), is put forward. ρ(c1) occurs between the contact metal and its underlying highly doped semiconductor layer (NDc) after alloying. ρc2 is brought about by a barrier appeared due to the concentration difference between the NDc and the active layer ND. If the alloying process is optimized and thus the NDc is very high, then ρ(c1) is very small and ρ(c2) gives the main contribution to ρc. In this case an inverse proportionality between ρc and NDcan be found, if NDc (Nc is the effective state density). When ND&gt; Nc, ρ(c2) can be neglected due to the disappearance of the barrier. In this case, ρc is determined by ρc1, which should depend only on NDc. Based on the above description, a theoretical deduction was carried out and the result not only can explain the experimental data of n-type GaAs ohmic contact very well, but also the experimental facts of p-type Si ohmic contact presented in the literatures. We believe that this model can also be extended to the case of other III-V compound semiconductors, such as p-type GaAs and P-type InP etc.

Mechanisms of Mo or Mo-Silicide/n+-Si Ohmic Contact Degradation Induced by High-Temperature Annealing

The degradation modes and mechanisms for Mo or Mo-silicide/n+-Si ohmic contacts induced by high-temperature annealing have been clarified and are classified as follows. 1) High resistance or insulating characteristics are due to oxygen contamination originating from contamination during electrode film deposition, adsorption in an electrode film from the atmosphere and knocked-on oxygen in silicon due to high-dose ion implantation through oxide for the formation of the doped region. 2) Current-flow induced open circuits at partial film cracks along the contact periphery. The film cracks result from volume shrinkage due to silicidation when the oxygen contamination is less severe. 3) Schottky barrier-like properties induced by dopant outdiffusion through silicide.

Multi-scan electron beam sintering of Al−Si OHMIC contacts: M. Finetti, S. Solmi and G. Soncini Solid-St. Electron.24, 539 (1981)

Multi-scan electron beam sintering of Al−Si OHMIC contacts: M. Finetti, S. Solmi and G. Soncini Solid-St. Electron.24, 539 (1981)

Multi-scan electron beam sintering of AlSi ohmic contacts

Experiments on sintering of AlSi ohmic contacts by scanning electron beam annealing are presented and discussed. Special test patterns have been used to measure the contact resistivity, while diode reverse current density has been checked to evaluate the junction leakage induced by the aluminum-silicon interaction during sintering. Electron beam annealing allows to obtain contact resistivities of the order of 10 −5 Ω cm 2, i.e. typical of conventional thermal sintering, while avoiding or strongly reducing the interdiffusion at the metal-silicon interface. High quality aluminum contacts on 0.3 μm phosphorus diffused junctions have been made by 20 KeV electron beam sintering at 0.25 A/cm 2 current density with negligible increase in junction leakage, while conventional thermal sintering, carried out for comparison, failed as expected due to heavy leakage induced by localized interdiffusion.